RL: Save intermediate model files and delete them after training

[magehrke]

Changes:

• Removes a bug, where the GPU crashed if a spike occurred during training
• The spike could not load the latest model, because no intermediate models where saved during training
• Set export_weights in rl_training.py to true
• Added function in fileio that removes all model files in the weight directory
• Calling the function at the end of training

TODO:

• if a spike occures before the first intermediate model is saved, the GPU will still crash. A fix to this is a little more challenging, because the rl_loop saves the models in a different format and we cannot reconstruct the file name that the trainer class needs.

[QueensGambit]

Thanks. Looks good to me!